Longitudinal to rotational motion

ABSTRACT

An apparatus for providing a conversion between longitudinal and rotational motion including a screw member having a thread having a constant angle and with individual ones of the opposing lands of the thread serving as the rolling surface for a cone member. The cone member is positioned within the lands of the thread and the cone member engages only one of the lands at a time along a line contact. Relative longitudinal movement between the screw member and the cone member is accomplished simultaneously with a relative helical movement between the screw member and the cone member and with the longitudinal motion and the helical motion between the screw member and the cone member occurring in either direction depending upon which of the lands is engaged by the cone member. The cone member also has a rotation about its central axis and such rotation occurs in a single direction. Other aspects of the invention include the use of the apparatus for converting between longitudinal and rotational motion as part of a propulsion device for a boat.

United States Patent Nicholson 1 Feb. 22, 1972 [54] LONGITUDINAL TOROTATIONAL MOTION James H. Nicholson, 5501 Onacrest Drive,

Primary Examiner--Andrew H. Farrell Attomey-Smyth, Roston & Pavitt [57]ABSTRACT An apparatus for providing a conversion between longitudinaland rotational motion including a screw member having a thread having aconstant angle and with individual ones of the opposing lands of thethread serving as the rolling surface for a cone member. The cone memberis positioned within the lands of the thread and the cone member engagesonly one of the, lands at a time along a line contact. Relativelongitudinal movement between the screw member and the cone member isaccomplished simultaneously with a relative helical movement between thescrew member and the cone member and with the longitudinal motion andthe helical motion between the screw member and the cone memberoccurring in either direction depending upon which of the lands isengaged by the cone member. The cone member also has a rotation aboutits central axis and such rotation occurs in a single direction.

Other aspects of the invention include the use of the apparatus forconverting between longitudinal and rotational motion as part of apropulsion device for a boat.

16 Claims, 5 Drawing Figures PAIENTEDHazanszz same M2 ,vrmawarfLONGITUDINAL TO ROTATIONAL MOTION The present invention is directed to adevice for providing for a conversion between longitudinal androtationalmotion. It is often desirable to provide for such a conversionfor different mechanical systems such as mechanical servosystems. Thepresent invention has the capability to convert the longitudinal motionto rotary motion with a minimum number of elements and therefore isextremely simple to manufacture. The apparatus of the present inventionmay provide for direct rotational output in accordance with alongitudinal input or alternatively a longitudinal output in accordancewith a rotational output. In addition to the conversion betweenlongitudinal and rotational motions, the present invention provides formore complex movements including combinations of longitudinal,rotational and helical motions.

The elements of the apparatus of the present invention are basically twoin number, and include a screw member having a thread having a constantangle extending around the central axis of the screw member and with thescrew member having opposing lands serving as rolling surfaces and withthe lands having a particular angular relationship relative to thecentral axis of the screw. Disposed between the lands of the thread is acone member which has substantially the same configuration as the landsof the screw so that the cone member may contact the lands of the screwalong a line contact. The cone member is positioned within the lands ofthe screw so that only one of the lands may be engaged by the conemember.

In order to provide for the conversion between longitudinal androtational motion, both the screw member and the cone member may havelongitudinal and rotational movements, and in addition there is arelative helical movement between the screw and the cone members duringthe conversion between the longitudinal and rotational motions.Specifically, the screw member may be rotatable about its central axisand may have longitudinal motion along its central axis. The cone membermay have rotational motion about its central axis and may havelongitudinal motion along an axis parallel to the central axis of thescrew member. Limiting one of the motions of either the screw member orthe cone member provides for various types of conversion betweenlongitudinal and rotational motion. As examples, the following types ofconversions may be possible.

The screw member may be maintained stationary both longitudinally androtationally. It is then possible to provide for a helical movement ofthe cone member in either direction by choosing which of the lands isengaged by the cone member and by rotating the cone member about itscentral axis.

The screw member may be fixed longitudinally but be allowed to rotateabout its central axis. By rotating the cone member in a singledirection the cone member may move longitudinally along a line parallelto the central axis of the screw member in either direction dependingupon which of the lands is engaged. The screw member will also rotate.As an alternative to the above, the screw member may be rotated and withthe cone member engaging one or the other of the lands to provide forthe longitudinal movement of the cone member along the line parallel tothe central axis of the screw member.

The screw member may be allowed to move longitudinally and to have arotation about its central axis. The cone member may be fixedlongitudinally so that an engagement of either of the lands by the conemember provides for a conversion between the longitudinal movement ofthe screw member and the rotation of the cone member. The cone memberrotates in a single direction even though the screw member is movedlongitudinally in both directions.

Other variations of movement may be accomplished whereby some of thecharacteristic movements of the screw and cone member may be ignored orbypassed. For example, the cone member may be held in a frame to move ina longitudinal direction in accordance with a rotation of the screwmember. The cone member may be used merely as a follower therebyignoring the rotational movement of the cone member and with thelongitudinal movement of the frame used in any desired manner.

A specific use of the conversion apparatus of the present invention isshown by a particular embodiment of the invention which uses thelongitudinal to rotational motion apparatus incorporated in a propulsiondevice for use with boats. It is to be appreciated, however, that theinvention is not to be limited to such use, and that any applicationswhich require the conversion between longitudinal and rotary motion mayprofitably use the present invention.

In the use of the invention as part of a propulsion device, the screwmember is positioned within a cylindrical shaft and may freely rotateabout its central axis within the shaft. An arm member extending withinthe shaft is rotatably coupled to the screw member so that if the arm ismoved in a longitudinal direction the screw member will follow. The conemember is positioned through an opening in the shaft to lie within thelands of the thread and the cone member, although allowed to freelyrotate, is fixed so as not to have any longitudinal movement.

A longitudinal movement of the arm and thereby the screw member inalternate directions provides for alternate engagement of the conemember with the opposite lands of thread. The screw member moveslongitudinally and rotates within the shaft. The cone member rotates ina single direction even though the screw member is being moved inalternate opposite longitudinal and rotational directions. A clampingmeans may be provided to clamp the structure to the boat and thevertical position may be adjusted to compensate for the various anglesof the side of the boat. A propeller is coupled to the cone member toprovide for movement of the boat in accordance with the actuation of thearm member. The clamping means may be such so as to allow the shaft tobe rotated within the clamping means so that the propeller may bepositioned in the water to provide for different directions of thrust toproduce a steering control as the boat is being moved by the propeller.

A clearer understanding of the invention will be had with reference tothe following description and drawings wherein:

FIG. 1 illustrates the motion conversion apparatus of the presentinvention as constructed for use as part of a propulsion device;

FIG. 2 illustrates the motion conversion apparatus of FIG. 1 enclosedwithin a shaft member and formed as a propulsion device; 1

FIG. 3 illustrates the motion conversion apparatus for the presentinvention formed as part ofa mechanical scrvosystem; FIG. 4 illustratesa view of the structure of FIG. 3 taken along line 4-4 of FIG. 3; and

FIG. 5 illustrates a view of the structure of FIG. 3 taken along line5-5 of FIG. 3.

In FIG. 1 a conversion apparatus of the present invention is shown whichmay be used as part of a propulsion device. Specifically, the apparatusof FIG. 1 includes a screw member 10 having a thread 12 having aconstant angle disposed around a central axis of the screw member 10.The thread 10 includes opposing land surfaces 14 and 16. A pair ofantifriction bearing surfaces 18 and 20 are disposed at either end ofthe screw member 10.

The upper end of the screw member 10 is rotatably mounted on an armmember 22. The rotation between the screw member 10 and the arm member22 may be accomplished using a bearing structure 24 which, as shown inFIG. 1, includes ball bearings. It is to be appreciated that types ofbearing structures other than ball bearings may be used and that theball bearings are illustrative only.

Disposed within the thread 12 between lands l4 and 16 is a cone member26 held at the end of a shaft 28. As can be seen, the cone member hasthe same angular relation to its central axis as do the lands l4 and 16to a line perpendicular to the central axis of the screw member. Thecone member 26 is positioned in such a manner that the cone member canonly contact one of the lands l4 and 16. Therefore, it is possible toengage the cone 26 with either but not both of the lands 14 and 16 alonga line contact. This eliminates any interference by dragging of thesurface opposite to that engaging a land.

Assuming that the screw member may be moved in either direction as shownby the arrow 30, and assuming first that the screw member is moved in anupward direction so that the cone member 26 engages the land 16, theangle of the lead of the thread 12 of the screw 10 causes a relativerotation between the cone member and the screw member 10. As shown inFIG. 1, the cone member 26 will rotate in the direction indicated by thearrow 32. If the screw member 10 is moved in a downward direction sothat the cone member 26 engages the land 14, this provides for anopposite rotation of screw member 10 relative to the direction ofrotation when the screw member is moved in the upward direction, but thecone member 26 will still rotate in the same direction as indicated byarrow 32. Even though the cone member 26 engages opposite lands of thethread 12 of screw member 10 depending upon the longitudinal directionof movement of the screw member 10, the cone member 26 always rotates inthe same direction.

The structure shown in FIG. 1 may be directly incorporated in apropulsion device for use with boats as shown in FIG. 2, and the sameelements of FIG. 1 are given similar reference characters in FIG. 2.Specifically in FIG. 2, the screw member 10 is shown disposed within acylindrical shaft member 100 wherein the antifriction surfaces 18 and 20contact the inner walls of the shaft member 100 and allow for the screwmember 10 to be moved both in a longitudinal direction within the shaft100 and also to rotate within the shaft 100 aroundthe arm member 22.

As shown in FIG. 2, the cone member 26 is maintained at a fixedlongitudinal position along the length of the shaft 100 by support means102. The shaft 28 is extended and has a threaded outer end. A propeller104 is mounted on the shaft 28 to freely rotate with the shaft 28 andthe cone 26. The propeller 104 is held in position on the shaft 28 by anut member 106. A baffle member 108 is shown disposed above thepropeller 104 to provide for a more efficient movement of the boat asthe propeller is rotated.

The arm member 22 is shown extending upward through the cylindricalshaft member 100 and is held in a central upward position by acylindrical member 110 which includes an outwardly extending flangeportion 112. The arm member 22 is actuated in a longitudinal directionwithin the shaft 100 using a handle member 114. The handle 114 may be ahollow tube having its ends enclosed by cap members 116 and 118. Acollar member 119 having end portions 120 and 122 surrounds the handle114. The end portion 120 and the shaft member 22 are coupled together ata pivot point 124 so as to allow for the handle 114 to pivot at thepoint 124. A link member 126 is coupled between the end portion 122 andthe flange 114, and the link member is coupled to the flange 114 and theend portion 122 at pivot points 128 and 130 so as to allow the handle114 to pivot around flange 112 while maintaining the shaft 22 in acentral location within the cylindrical shaft 100.

It can be seen, therefore, that the handle 114 may be moved up and downas shown by the arrow 132 so as to produce longitudinal movement of thearm 22 within the shaft 100 which in turn produce longitudinal movementof the screw member 10 within the shaft 100. As the screw member 10moves in a longitudinal direction, this produces a rolling motionbetween the cone 26 and the screw 10 which produces a rotation ofthepropeller 104. As explained above, the direction of rotation of thepropeller 104 is in a single direction even though the screw member ismoving up and down within the shaft 100, and even though the directionof rotation of the screw member 100 is reversing.

The propulsion device of FIG. 2 may be held onto a boat using a clampingapparatus including a pair of members 136 which are maintained in spacedrelationship using bolt member 138. Also, the members 136 are connectedon either side of the shaft 100 to an upper member 139 which iscylindrical and which surrounds the shaft l00. A lower cylindricalmember 140 is similar in configuration to the member 139. The members136 are coupled to the member 139 using-bolt 142. The upper member 139is restrained from sliding on the shaft by a spline 141 but is allowedto rotate about the shaft 100. The lower member may both slide androtate on the shaft 100 In order to control the angle at which thepropeller 104 is placed in the water relative to the boat 138, themembers 136 include a plurality of adjustment slots 144. A pair of rodmembers-146 are spring loaded in an upward direction by spring member148 and the rod members 146 interconnect the members 139 and 140. It canbe seen, therefore, that the rod member normally maintains the member140 in a upward direction. However, when it is desired to adjust theangle of the propeller 104 so as to compensate for different angles ofthe sides of the different boats, a plate member 150 may be pusheddownward to free a bolt member 152 from a particular one of the slots144, thereby allowing a different one of the slots 144 to be chosen or acomplete disengagement so as to swing the propeller out of the water.The angle of the propeller 104 in the water may therefore be adjusted bypositioning a desired one of the slots 144 over the bolt member 152.Finally, the entire structure may be held in place on the boat 134 usinga pair of screw clamps 154 with each clamp passing through a lowerportion ofone of the members I36.

7 It is also possible to steer the boat by rotating the shaft 100supporting the propeller within the members 139 and 140 using the handle114 so as to vary the direction of thrust of the propeller. Also, thehandle 114 may be slid through the collar member 119 and the shaftrotated so that the boat may be propelled backwards. In this way, theboat may be both steered and propelled using one had since both thesteering and the propelling are controlled by movements of the handle 114.

FIGS. 3, 4 and 5 illustrate apparatus of the present invention which maybe used for mechanical servocontrol. In FIGS. 3 through 5, elementswhich are similar to those shown in FIGS. 1 and 2 will be given the samereference characters. In FIGS. 3, 4 and.5, the screw member 10 includesa uniform thread 12 having lands l4 and 16. A cone member 26 is showndisposed within the lands 14 and 16 and the cone member may contact oneor the other, but not both of the lands 14 and 16. A pair of platemembers 200 and 202 are disposed at either end of the structure and areinterconnected by posts 204, 206 and 208. A bearing structure such as aball bearing 210 is mounted at one end adjacent the plate 200. A similarbearing structure 212 may be mounted adjacent the plate 202. A shaftmember 214 passes through the bearing 212 and is connected to the upperend of the screw 10. It can be seen, therefore, that a rotation of theshaft 214 provides for a rotation of the screw member 10 between theplates 200 and 202, and within the posts 204, 206 and 208.

A frame member 224 includes upper and lower arm portions 216 and 218which have openings 220 to enclose the posts 206and 208. It can be seen,therefore, that the arms 216 and 218 supporting the frame 224 can slidelongitudinally along the posts 206 and 208. The cone member 26 and theshaft 28 is maintained rotationally within the frame 224 using a bearingstructure such as ball bearing 222. It is to be appreciated that othertypes of bearings may be used and that ball bearings are illustrativeonly.

In order to have the cone member 26 engage a desired one of the lands 14and 16, a control structure may be included to effect a forced linecontact between the cone 26 and the desired one of the lands l4 and 16.For example, a free-rolling control cone 226 may be included within thethread lands and is rotatably mounted on a shaft 228 with a bearingstructure 230. A boss member 232 extends from the frame 224 and supportsa post 234. The arm 236 includes an opening 238 which is disposed arounda post 234. In addition, an opening 240 in the arm 236 is disposedaround the shaft 228. An upward motion of the control arm 236 moves thecontrol cone 226 into engagement with the land 114 and also moves thecone member 26 into engagement with the land 16. The position of thecontrol arm 236 may be reversed so that the cone 26 engages the upperland 14. It is to be appreciated that the control structure shown isillustrative only and that other forms of control structures may be usedto allow for the movement of the cone 26 into permanent or incrementalengagement with either of the lands 14 and 16.

In the example shown in FIGS. 3 through 5, the cone 26 engages the land16. It can be seen, therefore, that a rotation of the shaft 214 willprovide a longitudinal movement of the control cone 26 and the entireframe structure 224 along the rods 206 and 208. At the same time, thecontrol cone 26 rotates and such rotation may or may not be used as partof the servoing. The land 14 may be engaged by the control cone 26 byreversing the position of the control arm 236 so that the control cone226 engages the land 16 and at that time a rotation of the shaft member214 again provides for a longitudinal movement of the cone 26 and frame224 and also a rotation of shaft 28.

It is also possible to provide for the longitudinal movement of the cone26 and the frame member 224 by rotating the shaft 28 when the controlcone 26 is in engagement with either of the lands l4 and 16. Also, itcan be seen that the shaft 214 may be maintained stationary and arotation of the shaft 28 may be provided whereupon the cone 26 and theframe member 224 will not only move longitudinally but the entirestructure including the rods 204, 206 and 208 supporting the framemember 224 and the control cone 26 will rotate around the screw member10. It is, therefore, seen that a variety of movements may beaccomplished so that a plurality of mechanical servoing operations maybe produced. it is to be appreciated that geared surfaces may be used aspart of the thread and the cone so that a positive positioning isproduced to provide for a high degree of accuracy in the relativemovement of the motion conversion apparatus of the present invention. Itis to be appreciated that the above description is illustrative indescribing particular embodiments of the invention, but that theinvention is only to be limited by the appended claims.

I claim:

1. An apparatus for providing a conversion between longitudinal androtational motion, including a screw member having a thread having aconstant angle extending around the central axis of the screw memberwith the lands of the thread having particular angular relationships toa line perpendicular to the central axis of the screw,

a cone member rotatable about a central axis and positioned within thelands of the thread and with the cone member having an angularconfiguration relative to the central axis of the cone membersubstantially identical to the particular angular relationships of thelands of the thread to the line perpendicular to the central axis of thescrew and with the size of the cone member smaller than the distancesbetween the lands of the thread to allow the outer surface of the conemember to engage either land of the thread along a line contact, and

the screw member and cone member providing for relative longitudinalmovement and rotational movements in first directions when the conemember engages one of the lands of the thread and with the screw memberand cone member providing for relative longitudinal and rotationalmovements in second directions when the cone member engages the other ofthe lands of the thread and with a rotation of the cone member about thecentral axis in the same direction when the cone member engages eitherof the lands of the thread.

2. The apparatus of claim I wherein the screw member is mounted forrotation about its central axis to provide for the relative longitudinalmovement between the screw member and the cone member along a lineparallel to the central axis of the screw member.

3. The apparatus ofclaim 1 wherein the screw member is maintained in afixed longitudinal position to provide for longitudinal and rotationalmovement of the cone member.

4. The apparatus of claim 1 wherein the screw member is mounted forrotation about its central axis and is maintained in a fixedlongitudinal position to provide for longitudinal movement of the conemember along a line parallel to the central axis of the screw member.

5. The apparatus of claim 1 wherein the screw member is mounted forrotation about its central axis and the cone member is maintained in afixed longitudinal position to provide for rotation of the cone memberin the same direction in accordance with longitudinal movement ofthescrew member in either direction.

6. The apparatus of claim 5 wherein the screw member rotates and ismoved longitudinally within a cylindrical shaft member and the conemember is mounted for rotation at a fixed longitudinal position alongthe shaft member.

7. The apparatus of claim 6 wherein an activating arm is coupled to thescrew member to provide for the longitudinal movement of the screwmember in both directions and a propeller is coupled to the cone memberto provide for rotations of the propeller in the same direction inaccordance with actuations of the actuating arm in both directions.

8. An apparatus for'providing a conversion between longitudinal androtational motion including a screw member having a thread extendingalong at least a portion of the length of the screw member and havinglands forming the sidewalls of the thread,

a first cone member positioned within the lands of the thread at alocation to provide for engagement between the outer surface of the conemember and one of the lands of the thread and with the cone memberincluding a shaft extending from the cone, and

means for providing engagement between the cone member and one of thelands of the thread of the screw members for producing relativelongitudinal movement between the screw member and the cone member intwo directions and for providing rotation ofthe shaft member.

9. The apparatus of claim 8 wherein the screw member is maintained in afixed longitudinal position and is rotatable about a central axis of thescrew member to provide for longitudinal movement of the first conemember and rotation of the screw member.

10. The apparatus ofclaim 8 wherein the cone member is maintained in afixed longitudinal position and the screw member is rotatable about acentral axis of the screw member to provide for the rotation of thefirst cone member and longitudinal movement of the screw member.

11. The apparatus of claim 8 wherein the last mentioned means includesat least a second cone member positioned within the lands of the threadand interconnected with the first cone member and with an engagement ofthe second cone member with one of the lands of the thread producing anengagement of the first cone member with an opposite one of the lands ofthe thread.

12. The apparatus of claim 8 wherein the screw member is rotatablydisposed within a cylindrical shaft member and is moved in alongitudinal direction within the cylindrical shaft member by anactuating arm and wherein the first cone member is maintained in a fixedlongitudinal position along the shaft member to provide rotations of thefirst cone member in accordance with movements of the actuating arm.

13. The apparatus of claim 8 additionally including clamping means forclamping the apparatus to a boat and additionally including a propellercoupled to the shaft member to provide a propulsion device.

14. An apparatus for providing a conversion between longitudinal androtational motions, including a cylindrical shaft member,

a screw member disposed within the shaft member and having a uniformthreaded portion with opposing lands,

an arm member extending within the cylindrical shaft and rotatablycoupled to the screw member,

means coupled to the arm member for providing longitudinal movements ofthe arm and screw members within the shaft,

a cone member mounted at a position along the shaft and with the conemember extending through an opening in the shaft and positioned withinthe lands of the thread for engagement with one or the other of thelands of the thread in accordance with the direction of longitudinalmovement of the screw member and with the cone

1. An apparatus for providing a conversion between longitudinal androtational motion, including a screw member having a thread having aconstant angle extending around the central axis of the screw memberwith the lands of the thread having particular angular relationships toa line perpendicular to the central axis of the screw, a cone memberrotatable about a central axis and positioned within the lands of thethread and with the cone member having an angular configuration relativeto the central axis of the cone member substantially identical to theparticular angular relationships of the lands of the thread to the lineperpendicular to the central axis of the screw and with the size of thecone member smaller than the distances between the lands of the threadto allow the outer surface of the cone member to engage either land ofthe thread along a line contact, and the screw member and cone memberproviding for relative longitudinal movement and rotational movements infirst directions when the cone member engages one of the lands of thethread and with the screw member and cone member providing for relativelongitudinal and rotational movements in second directions when the conemember engages the other of the lands of the thread and with a rotationof the cone member about the central axis in the same direction when thecone member engages either of the lands of the thread.
 2. The apparatusof claim 1 wherein the screw member is mounted for rotation about itscentral axis to provide for the relative longitudinal movement betweenthe screw member and the cone member along a line parallel to thecentral axis of the screw member.
 3. The apparatus of claim 1 whereinthe screw member is maintained in a fixed longitudinal position toprovide for longitudinal and rotational movement of the cone member. 4.The apparatus of claim 1 wherein the screw member is mounted forrotation about its central axis and is maintained in a fixedlongitudinal position to provide for longitudinal movement of the conemember along a line parallel to the central axis of the screw member. 5.The apparatus of claim 1 wherein the screw member is mounted forrotation about its central axis and the cone member is maintained in afixed longitudinal position to provide for rotation of the cone memberin the same direction in accordance with longitudinal movement of thescrew member in either direction.
 6. The apparatus of claim 5 whereinthe screw member rotates and is moved longitudinally within acylindrical shaft member and the cone member is mounted for rotation ata fixed longitudinal position along the shaft member.
 7. The apparatusof claim 6 wherein an activating arm is coupled to the screw member toprovide for the longitudinal movement of the screw member in bothdirections and a propeller is coupled to the cone member to provide forrotations of the propeller in the same direction in accordance withactuations of the actuating arm in both directions.
 8. An apparatus forproviding a conversion between longitudinal and rotational motionincluding a screw member having a thread extending along at least aportion of the length of the screw member and having lands forming thesidewalls of the thread, a first cone member positioned within the landsof the thread at a location to provide for engagement between the outersurface of the cone member and one of the lands of the thread and withthe cone member including a shaft extending from the cone, and means forproviding engagement between the cone member and one of the lands of thethread of the screw members for producing relative longitudinal movementbetween the screw member and the cone member in two directions and forproviding rotation of the shaft member.
 9. The apparatus of claim 8wherein the screw member is maintained in a fixed longitudinal positionand is rotatable about a central axis of the screw member to provide forlongitudinal movement of the first cone member and rotation of the screwmember.
 10. The apparatus of claim 8 wherein the cone member ismaintained in a fixed longitudinal position and the screw member isrotatable about a central axis of the screw member to provide for therotation of the first cone member and longitudinal movement of the screwmember.
 11. The apparatus of claim 8 wherein the last mentioned meansincludes at least a second cone member positioned within the lands ofthe thread and interconnected with the first cone member and with anengagement of the second cone member with one of the lands of the threadproducing an engagement of the first cone member with an opposite one ofthe lands of the thread.
 12. The apparatus of claim 8 wherein the screwmember is rotatably disposed within a cylindrical shaft member and ismoved in a longitudinal direction within the cylindrical shaft member byan actuating arm and wherein the first cone member is maintained in afixed longitudinal position along the shaft member to provide rotationsof the first cone member in accordance with movements of the actuatingarm.
 13. The apparatus of claim 8 additionally including clamping meansfor clamping the apparatus to a boat and additionally including apropeller coupled to the shaft member to provide a propulsion device.14. An apparatus for providing a conversion between longitudinal androtational motions, including a cylindrical shaft member, a screw memberdisposed within the shaft member and having a uniform threaded portionwith opposing lands, an arm member extending within the cylindricalshaft and rotatably coupled to the screw member, means coupled to thearm member for providing longitudinal movements of the arm and screwmembers within the shaft, a cone member mounted at a position along theshaft and with the cone member extending through an opening in the shaftand positioned within the lands of the thread for engagement with one orthe other of the lands of the thread in accordance with the direction oflongitudinal movement of the screw member and with the cone memberrotating in a single direction with engagement of the cone member withone or the other of the lands of the thread.
 15. The apparatus of claim14 additionally including means for mounting the apparatus on a boat andadditionally including a propeller coupled to the cone member to providea propulsion device for a boat. 16 The apparatus of claim 14 wherein themeans for mounting allows the shaft to be rotated to provide for arudder control.